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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Claise 3 Internet-Draft J. Clarke 4 Updates: 7950 (if approved) Cisco Systems, Inc. 5 Intended status: Standards Track J. Shakir 6 Expires: May 3, 2018 Google 7 J. D'Souza 8 AT&T 9 October 30, 2017 11 New YANG Module Update Procedure 12 draft-clacla-netmod-yang-model-update-00 14 Abstract 16 This document specifies a new YANG module update procedure in case of 17 non backward-compatible changes, as an alternative proposal to the 18 YANG 1.1 specifications. This document updates RFC 7950. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on May 3, 2018. 37 Copyright Notice 39 Copyright (c) 2017 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. The Problems . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2.1. Slow Standardization . . . . . . . . . . . . . . . . . . 3 57 2.2. Some YANG Modules are Not Backward Compatible . . . . . . 3 58 2.3. A Zoo of YANG Modules . . . . . . . . . . . . . . . . . . 3 59 2.4. YANG Modules Obsolete Relationship . . . . . . . . . . . 4 60 2.5. YANG Module Transition Strategy . . . . . . . . . . . . . 5 61 3. The Solution . . . . . . . . . . . . . . . . . . . . . . . . 6 62 3.1. SEMVER Semantic Versioning . . . . . . . . . . . . . . . 6 63 3.2. Updating the YANG 1.1 Specifications . . . . . . . . . . 9 64 3.3. The Derived Semantic Version . . . . . . . . . . . . . . 9 65 4. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 70 7.2. Informative References . . . . . . . . . . . . . . . . . 10 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 73 1. Introduction 75 The YANG data modeling language [RFC7950] specifies strict rules for 76 updating YANG modules (see section 11 "Updating a Module"). Citing a 77 few of the relevant rules for this document: 79 1. "As experience is gained with a module, it may be desirable to 80 revise that module. However, changes to published modules are 81 not allowed if they have any potential to cause interoperability 82 problems between a client using an original specification and a 83 server using an updated specification." 85 2. "Note that definitions contained in a module are available to be 86 imported by any other module and are referenced in "import" 87 statements via the module name. Thus, a module name MUST NOT be 88 changed. Furthermore, the "namespace" statement MUST NOT be 89 changed, since all XML elements are qualified by the namespace." 91 3. "Otherwise, if the semantics of any previous definition are 92 changed (i.e., if a non-editorial change is made to any 93 definition other than those specifically allowed above), then 94 this MUST be achieved by a new definition with a new identifier." 96 What are the consequences? 97 1. Ideally, the YANG module names should not be changed due the 98 importance of not changing the automation code in case of import 99 statements or service composition at the orchestrator. 101 2. When the same YANG module name is kept, the new YANG module 102 revision must always be updated in a backward-compatible way. 104 2. The Problems 106 This section lists a series of problems, hopefully listed in a 107 logical order, which leads to the solution in the next section. 109 2.1. Slow Standardization 111 The conclusions drawn in the introduction lead to the logical 112 conclusion that the standardized YANG modules have to be perfect day 113 one (at least the structure), which in turns, might explain why all 114 the IETF YANG modules take so long to standardize. Shooting for 115 perfection (at least the structure) is obviously a noble goal but, if 116 the perfect standard comes too late, it doesn't help the industry. 118 2.2. Some YANG Modules are Not Backward Compatible 120 As we learn from our mistakes, we're going to face more and more non 121 backward-compatible YANG modules. An example is the YANG data model 122 for L3VPN service delivery [RFC8049], which, based on implementation 123 experience, must be updated in a non backward-compatible way with 124 draft-wu-l3sm-rfc8049bis [I-D.wu-l3sm-rfc8049bis]. 126 While Standardized Development Organization YANG modules are 127 obviously better for the industry, we must recognize that many YANG 128 modules are actually generated YANG modules (for example, from 129 internal database), also known as native YANG modules, or vendor 130 modules [RFC8199]. From time to time, the new YANG modules are not 131 backward-compatible. 133 In such cases, it would be better to indicate how backward-compatible 134 YANG modules are. 136 2.3. A Zoo of YANG Modules 138 Even if we focus on the IETF, we have to observe that many Standard 139 Development Organizations, opensource fora, and vendors develop YANG 140 modules develop YANG modules. This should be considered a success 141 for an IETF developed technoogy. However, the operators are faced 142 with this problem: how to select the YANG modules to take into 143 account for their service developments. 145 The site (and the YANG catalog that it 146 provides: YANG module for yangcatalog.org, 147 [I-D.clacla-netmod-model-catalog]) is an attempt to become a 148 reference for all YANG modules available in the industry, for both 149 YANG developers to search on what exists already) and for operators 150 (to discover the more mature YANG models to automate services). This 151 YANG catalog should not only contain pointers to the YANG modules 152 themselves, but also contain metadata related to those YANG modules: 153 What is the module type (service model or not?); what is the maturity 154 level? (e.g., for the IETF: is this an RFC, a working group document 155 or an individual draft?); is this module implemented?; who is the 156 contact?; is there open-source code available? And we expect many 157 more in the future. The industry has begun to understand that the 158 metadata related to YANG models become equally important as the YANG 159 models themselves. 161 The yangcatalog.org instantiation of the catalog provides a means for 162 module authors and vendors implementing modules to upload their 163 metadata, which is then searchable via an API, as well as using a 164 variety of web-based tools. The instructions for contributing and 165 searching for metadata can be found at . 168 The issue is actually the number of YANG modules the operators are 169 offered. At the time of writing these lines, the number of unique 170 YANG modules in the catalog is exactly 2596 (and the number keeps 171 growing), while the IETF has standardized or is busy standardizing a 172 small subset of those. Therefore, it's important to distinguish the 173 relevant YANG modules with the pack and to understand the 174 relationship between the YANG modules. 176 2.4. YANG Modules Obsolete Relationship 178 So the operators use the yangcatalog.org to discover which YANG 179 modules they can use NOW. They base their selection not only on the 180 YANG module content, but also on the related metadata. When faced 181 with the zoo of the YANG modules, it's difficult to understand the 182 relationship between YANG modules. As an example: how could an 183 operator discovers that a YANG-MODULE-B obsoletes YANG-MODULE-A? 184 Indeed, both have different YANG module names. The only available 185 information is an "obsolete" tag in the published RFC containing 186 YANG-MODULE-B: this tag would point to YANG-MODULE-A. In the world 187 of automation, going through a published RFC as a level of 188 indirection to understand the YANG module obsolete relationship is a 189 non starter. Food for thought: the IETF should stop thinking that 190 the metric for success is an RFC number, as opposed to the contained 191 YANG module(s). 193 We need an automatic way to discover that a YANG-MODULE-B obsoletes 194 YANG-MODULE-A, so that YANG-MODULE-A should not be given any 195 attention. 197 The following example is not an automatic way. 199 description 200 "This YANG module defines a generic service configuration 201 model for Layer 3 VPNs. This model is common across all 202 vendor implementations. This obsoletes the RFC8049 YANG 203 module, ietf-l3vpn-svc@2017-01-2"; 204 revision 2017-09-14 { 205 description 206 "First revision of RFC8049."; 207 reference 208 "RFC xxxx: YANG Data Model for L3VPN Service Delivery"; 210 Along the same lines, going through an offline tool such as the 211 yangcatalog.org, in order to discover the obsolete relationship is a 212 possible automatic way, but not ideal. 214 2.5. YANG Module Transition Strategy 216 Let's assume for a moment that we change the YANG module, with the 217 specific example of the ietf-routing, which some propose to update to 218 ietf-routing-2. 220 Here are all the ietf-routing dependent YANG modules (those modules 221 that depend on ietf-routing) . So many 224 YANG modules. 226 Let's look at the difference for ietf-routing-2: 227 . 231 Changing the module name from ietf-routing to ietf-routing-2 implies 232 that the we have to warn all draft authors of ietf-routing YANG 233 dependent modules. Firstly, to make sure they are aware of ietf- 234 routing-2 (publishing a RFC8022bis mentioning in the module 235 description that this module is not compatible with the NMDA 236 architecture, and providing a pointer to ietf-routing-2 ... is not an 237 automatic way... so barely useful). And secondly, to ask them to 238 change their import (or service composition) to ietf-routing-2. 239 Hopefully, in the ietf-routing case, all dependent YANG modules are 240 part of the IETF, so the communication is a manageable. 242 Changing the ietf-interfaces YANG module name would be a different 243 challenge, as it's used throughout the industry: 244 248 3. The Solution 250 The solution is composed of two mandator aspects, a semantic 251 versioning YANG extension and an update to RFC7950. An optional 252 additional check, validating the semantic versioning from a syntact 253 point of view, can either assist in determining the correct semantic 254 versioning values, or can help in determining the values for YANG 255 modules that don't support this extension. 257 3.1. SEMVER Semantic Versioning 259 The semantic versioning solution proposed here as already been 260 proposed in [I-D.openconfig-netmod-model-catalog] (cut/paste here 261 with the authors permission)which itself is based on 262 [openconfigsemver]. The goal is to indicate the YANG module 263 backwards (in)compatibility, following semver.org semantic versioning 264 [semver]: 266 MAJOR is incremented when the new version of the specification is 267 incompatible with previous versions. 269 MINOR is incremented when new functionality is added in a manner 270 that is backward-compatible with previous versions. 272 PATCH is incremented when bug fixes are made in a backward- 273 compatible manner. 275 // extension statements 276 extension openconfig-version { 277 argument "semver" { 278 yin-element false; 279 } 280 description 281 "The OpenConfig version number for the module. This is 282 expressed as a semantic version number of the form: 283 x.y.z 284 where: 285 * x corresponds to the major version, 286 * y corresponds to a minor version, 287 * z corresponds to a patch version. 288 This version corresponds to the model file within which it is 289 defined, and does not cover the whole set of OpenConfig models. 290 Where several modules are used to build up a single block of 291 functionality, the same module version is specified across each 292 file that makes up the module. 294 A major version number of 0 indicates that this model is still 295 in development (whether within OpenConfig or with industry 296 partners), and is potentially subject to change. 298 Following a release of major version 1, all modules will 299 increment major revision number where backwards incompatible 300 changes to the model are made. 302 The minor version is changed when features are added to the 303 model that do not impact current clients use of the model. 305 The patch-level version is incremented when non-feature changes 306 (such as bugfixes or clarifications to human-readable 307 descriptions that do not impact model functionality) are made 308 that maintain backwards compatibility. 310 The version number is stored in the module meta-data."; 311 } 313 The extension would typically be used this way: 315 module yang-module-name { 317 yang-version "1"; 318 namespace "name-space"; 319 prefix "prefix-name"; 321 import openconfig-extensions { prefix "oc-ext"; } 323 organization 324 "to be completed"; 326 contact 327 "to be completed"; 329 description 330 "to be completed"; 332 oc-ext:openconfig-version "1.1.2"; 334 revision 2017-10-30 { 335 description 336 "Change the module structure"; 337 reference "1.1.2"; 338 } 340 revision 2017-07-30 { 341 description 342 "Fixed unprintable character"; 343 reference "0.1.2"; 344 } 346 revision 2017-04-03 { 347 description 348 "Update copyright notice."; 349 reference "0.1.1"; 350 } 352 revision 2017-01-26 { 353 description 354 "Initial module for inet types"; 355 reference "0.1.0"; 356 } 358 //YANG module definition starts here 360 See also "Semantic Versioning and Structure for IETF Specifications" 361 [I-D.claise-semver] for a mechanism to combine the semantic 362 versioning, the github tools, and a potential change to the IETF 363 process. 365 3.2. Updating the YANG 1.1 Specifications 367 RFC 7950 section 11, must be updated to express: 369 "As experience is gained with a module, it may be desirable to revise 370 that module. Changes to published modules are allowed, even if they 371 have some potential to cause interoperability problems, at the 372 condition that the semantic versioning change are clearly indicated 373 based on the SEMVER YANG extension." 375 3.3. The Derived Semantic Version 377 The YANG catalog contains not only the most up-to-date YANG module 378 revision of a given module, but keeps all previous revisions as well. 379 With APIs in mind, it's important to understand whether different 380 YANG module revisions are backward compatible (this is specifically 381 imported for native YANG modules, i.e. the ones where generated-from 382 = native), even for the YANG modules that don't support the YANG 383 extension specified in this document. 385 Two distinct leaves in the YANG module 386 [I-D.clacla-netmod-model-catalog] contains this semver semantic: 388 the semantic-version leaf contains the value reported as metadata 389 by a specific YANG module. 391 the derived-semantic-version leaf is established by examining the 392 the YANG module themselves. As such, only the YANG syntax, as 393 opposed to the implementation changes that lead some some semantic 394 changes. 396 The derived-semantic-version is based on "pyang --check-update-from", 397 which checks the backward compatibility from a syntax point of view. 399 Note that the absolute numbers in the semantic-version and derived- 400 semantic-version are actually meaningless: the difference between two 401 YANG module semver fields should be looked at. 403 4. Contributors 405 Anees Shaikh, Google 407 5. Security Considerations 409 To be completed 411 6. IANA Considerations 413 No IANA action is requested. 415 7. References 417 7.1. Normative References 419 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", 420 RFC 7950, DOI 10.17487/RFC7950, August 2016, 421 . 423 7.2. Informative References 425 [I-D.clacla-netmod-model-catalog] 426 Clarke, J. and B. Claise, "YANG module for 427 yangcatalog.org", draft-clacla-netmod-model-catalog-02 428 (work in progress), October 2017. 430 [I-D.claise-semver] 431 Claise, B., Barnes, R., and J. Clarke, "Semantic 432 Versioning and Structure for IETF Specifications", draft- 433 claise-semver-01 (work in progress), July 2017. 435 [I-D.openconfig-netmod-model-catalog] 436 Shaikh, A., Shakir, R., and K. D'Souza, "Catalog and 437 registry for YANG models", draft-openconfig-netmod-model- 438 catalog-02 (work in progress), March 2017. 440 [I-D.wu-l3sm-rfc8049bis] 441 Wu, Q., Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG 442 Data Model for L3VPN Service Delivery", draft-wu-l3sm- 443 rfc8049bis-09 (work in progress), October 2017. 445 [openconfigsemver] 446 "Semantic Versioning for Openconfig Models", 447 . 449 [RFC8049] Litkowski, S., Tomotaki, L., and K. Ogaki, "YANG Data 450 Model for L3VPN Service Delivery", RFC 8049, 451 DOI 10.17487/RFC8049, February 2017, 452 . 454 [RFC8199] Bogdanovic, D., Claise, B., and C. Moberg, "YANG Module 455 Classification", RFC 8199, DOI 10.17487/RFC8199, July 456 2017, . 458 [semver] "Semantic Versioning 2.0.0", . 460 Authors' Addresses 462 Benoit Claise 463 Cisco Systems, Inc. 464 De Kleetlaan 6a b1 465 1831 Diegem 466 Belgium 468 Phone: +32 2 704 5622 469 Email: bclaise@cisco.com 471 Joe Clarke 472 Cisco Systems, Inc. 473 7200-12 Kit Creek Rd 474 Research Triangle Park, North Carolina 475 United States of America 477 Phone: +1-919-392-2867 478 Email: jclarke@cisco.com 480 Rob Shakir 481 Google 482 1600 Amphitheatre Pkwy 483 Mountain View, CA 94043 484 United States of America 486 Email: rjs@rob.sh 488 Kevin D'Souza 489 AT&T 490 200 S. Laurel Ave 491 Middletown, NJ 492 United States of America 494 Email: kd6913@att.com